1. Field of the Invention
This invention relates to an ink jet recording apparatus designed such that recording liquid can be poured into a recording liquid container.
2. Description of the Prior Art
In the conventional ink jet recording apparatus using an open system supply mechanism, as shown in FIG. 1 of the accompanying drawings, a supply path 2 is connected to one end of a recording head 1 comprising a piezoelectric element or the like to receive the supply of recording liquid 4 from a recording liquid container 3. The upper surface of the container 3 is formed with a vent hole 5 for maintaining the interior of the container 3 always at atmospheric pressure. The recording liquid 4 in the container 3 always reaches the tip end of the recording head 1 through the supply path 2 and, in response to an electrical signal applied to the piezoelectric element of the recording head 1, liquid drops 6 are discharged from the tip end, namely, the discharge orifice 1A, of the recording head 1, whereby characters or the like are printed on printing paper. The decrease of the recording liquid discharged as liquid drops 6 is successively supplemented from the container 3 through the supply path due to the surface tension of the discharge orifice 1A of the recording head 1 and the difference in level between the recording liquid in the container 3 and the recording head 1 and thus, the recording liquid 4 always reaches the discharge orifice 1A of the recording head 1.
The conventional ink jet recording apparatus of such type suffers from the following problems. That is, where the object into which the ink jet recording apparatus is incorporated is a portable desk top calculator or a small typewriter, if the apparatus body is inclined during the carrying of the calculator or the typewriter, the difference in level of the recording liquid between the container 3 and the discharge orifice 1A sometimes is not maintained at a proper value because there is a certain degree of distance between the container 3 and the tip end of the recording head 1. In such case, the meniscus of the recording liquid formed by the discharge orifice 1A may retreat inwardly of the supply path 2 or the recording liquid may leak from the discharge orifice 1A. When the meniscus has retreated, it is necessary to recover it as by applying a pressure from the container 3 side and, when the recording liquid has leaked, it contaminates the interior of the apparatus. Such recovery of the meniscus during each transportation or the leakage of the recording liquid in the interior of the apparatus is very awkward to the operator and is not desirable.
Also, when vibration or shock is imparted to the apparatus or when the recording head 1 strikes against the printing end portion at high speed, the aforementioned leakage of the recording liquid or the retreat of the meniscus is more liable to occur. That is, when vibration or shock is imparted to the apparatus body or the recording head 1 or the supply path 2, the meniscus at the discharge orifice 1A may be destroyed thereby, so that it may leak as liquid drops to the outside or may retreat inwardly of the supply path 2. At this time, where there is an improper difference in level between the container 3 and the recording head 1, the meniscus is liable to be destroyed and, once it is destroyed, it cannot readily be restored to its original state and the liquid continuously leaks to the outside or the meniscus retreats inwardly of the supply path 2 to a position whereat the balance between the level difference and the surface tension can be kept. Such vibration or shock always occurs where the recording is effected by reciprocating the recording head 1 relative to a recording medium, for example, printing paper, and therefore the presence of an improper level difference between the container 3 and the recording head 1 is fatal. Also, in order that the meniscus may not be destroyed, the speed of reciprocal movement of the recording head 1 is limited and thus, high-speed printing is difficult.
Another problem occurs when bubbles have come into the supply path 2. That is, if bubbles are present only in the supply path 2, the discharging performance will not be hindered, whereas when the bubbles have moved to the recording head 1 with the movement of the recording liquid, the discharge becomes unsatisfactory. Especially, in an apparatus utilizing the deforming action of an electro-mechanical converter member as the discharge drive source of the recording head 1, the energy created by deformation is absorbed into bubbles and such energy is not transmitted to the recording liquid, but the discharge of the recording liquid from the recording head 1 is completely stopped, thus making continuous stable printing difficult.
Applicant has previously proposed an ink jet recording apparatus which intends to overcome the problems in such open system supply mechanism.
FIGS. 2A and 2B of the accompanying drawings show an example of the proposed ink jet recording apparatus. Reference numeral 10 designates a recording head, and the recording head 10 and a recording liquid container 11 are made integral with each other and contained in a single container 12. The container 12 is fixed to a carriage 13 which in turn in slidably mounted on a shaft 14 and effects the printing while moving along the widthwise direction of printing paper. The recording head 10 can comprise a piezoelectric element 15, a nozzle portion 16, a discharge orifice 17 and a supply tube 18. This supply tube 18 extends from the recording head body to the interior of the recording liquid container 11 while assuming an L-shape, so that the recording liquid 19 in the recording liquid container 11 is directed into the recording head 10 through the supply tube 18. Also, this supply tube 18 is fixed to a wall 20 covering the upper portion of the container 12, so that the supply tube 18 is not moved by vibration or shock. Designated by 21 is a vent hole of the recording liquid container 11 for maintaining the pressure in the tank 11 always at atmospheric pressure. Designated by 22 and 23 are connectors for supplying an electrical signal from the outside to the piezoelectric element 15 forming the recording head 10. The piezoelectric element 15 and the connectors 22, 23 are connected by signal lines, not shown. Design is made such that the distance between the discharge orifice 17 provided at the end of the nozzle portion 16 and the distal end 18A of the supply tube 18 is set to a suitable distance.
According to the ink jet recording apparatus constructed as described above, the recording head 10 and the recording liquid container 11 are contained as a unit in the single container 12, and the supply tube 18 for supplying the recording liquid to the recording head 10 is determined to an appropriate length and inserted into the recording liquid container 11 and thus, the recording liquid never leaks from the recording head 10 or the meniscus in the discharge orifice 17 never retreats inwardly of the supply tube 18 due to the inclination, vibration or shock as previously described.
However, it has been found that such an ink jet recording apparatus still suffers from problems.
One of the problems is that in the case of a compact calculator in which high printing speed is required, the reciprocally moved drive carriage portion should desirably be light in weight from the viewpoint of the performance of the drive motor and therefore, the recording liquid stored in the recording liquid container is restricted in weight. Accordingly, in FIG. 2, the volume of the recording liquid container 11 must be minimized to provide a light weight container and realize high-speed printing. However, if the volume of the recording liquid container 11 is reduced, the recording liquid in that container will be exhausted in a short time and thus, the container 12 containing the recording head 10 and the recording liquid container 11 as a unit must be frequently replaced by a new one, but undesirably this means a higher maintenance expense in the case of desk top calculators provided with a printer or typewriters directed to individual users, because the recording head is expensive.